Epithelial cells generally require polarization in two axes for their function, the ubiquitous apical-basal polarity and a second axis within the plane of the epithelium, called Planar Cell Polarity (PCP). Both polarity and ordered patterning are established during organogenesis. Typical PCP examples include aspects of mammalian skin or internal organs, like the inner ear epithelium with its sensory cilia. In Drosophila, and insects in general, all cuticular structures show PCP features. The establishment of PCP in Drosophila serves as a paradigm to study PCP determination in development and disease. PCP is thought to be coordinated by long-range signals, resulting in the graded activity of the Frizzled (Fz) receptor (with Wnt family members as their ligands) and its associated signaling cascade (Fz/PCP signaling). This Fz/PCP signaling pathway is conserved throughout evolution and regulates many aspects of coordinated cellular polarization, including directed cell migration during mammalian gastrulation. Wnt-Fz/PCP signaling is distinct from the canonical Wnt-Fz/2-catenin pathway. The regulation of signaling specificity between the two pathways activated by the same receptor(s) is critical for development or disease but not yet understood. Similarly, the link between Fz/PCP signaling and the resulting cellular responses, including cytoskeletal organization or specific transcriptional events are only poorly dissected. The scope of this application is to investigate the mechanistic and functional interactions among the core Fz/PCP determinants, and the integration of newly identified PCP genes (isolated through ongoing genomic screens). Their function in Fz/PCP signaling and in general cellular polarization events will be investigated genetically, biochemically, and at the cell biological level. A combination of in vivo studies in Drosophila, cell culture analyses in mammalian and Drosophila cells, and biochemical experiments will be performed to achieve these goals. The global long-range polarization events will be given special attention. The processes of PCP establishment and Wnt/Fz signaling have been linked to several medical abnormalities, including deafness, cancer (several components of the pathway are proto-oncogenes or tumor suppressors), poly cystic kidney disease, and ciliopathies in general. Thus the information acquired in this application will both advance our understanding of cellular polarization and patterning, and will be of medical relevance in several disease contexts. PUBLIC HEALTH RELEVANCE: Cellular polarity is an essential feature of organogenesis and development and tissue function in general. The regulation and maintenance of the epithelial planar cell polarity (PCP) feature is linked to many diseases, ranging from ciliopathies and deafness, to cancer (e.g. several polarity determinants are tumor suppressors or proto-oncogenes). This application addresses the molecular regulation of PCP establishment; the information acquired here is of high significance for many medical disorders.